Attic insulation - vapor barrier connection

Hello, I am currently insulating our attic. The house (bungalow) was built in 2011. The ceiling is insulated including a vapor barrier foil. I am using a 22 cm between-rafter insulation for this.

Now to the problem. How do I best connect the vapor barrier foil from the attic insulation to the lower vapor barrier foil? If I do not make this connection, I fear that wind will blow through there and heat will be lost.

To clarify, here are three pictures:

In the second picture, you can see that the wall ends somewhat below the attic height. Behind the wall is a cavity which I would fill with insulation material.

In the third picture, you can see the floor insulation (below that is the vapor barrier foil). For inspection, I have cut a hole here.

Do I have to remove the floorboards here in order to glue the vapor barrier coming from above to the lower vapor barrier? Is there any other solution?

Hello Sebastian,
in the next few months I also have the intermediate insulation to do. The house used to have a flat roof, so I assume a similar structure in the intermediate ceiling as you do. Since a marten has often been active in the roof so far, I first installed a closure there.
Then the insulation goes on, and then I staple the vapor barrier foil to the floor with battens.
Why do you want to connect the new vapor barrier with the old vapor barrier?
Best regards from
Babenhausen

And don't forget the ventilation of the attic.

@ If the vapor barrier on the upper floor is not sealed to the vapor barrier on the ground floor, then I have an area in the middle of the house that is not protected from the wind. The wind can penetrate here, leading to heat loss and a cold floor in the attic.

@ Can you explain that in more detail? Is the ventilation flap on the window sufficient here? (4 pieces available)

You need to ensure air exchange, because otherwise introduced moisture cannot escape and damages are likely. And the moisture is definitely coming. Now most likely the entire ridge is open. The necessary air exchange can be calculated, whether the flaps are sufficient you have to decide yourself.

Yes, that is clear. Now I am left with the question of how to connect the vapor barrier foil most easily together?